1. Field of the Invention
The present invention relates to the field of network communications. More specifically, the present invention relates to the use of a content routing service protocol to provide distributed Layer 7 switching in a computer network.
2. The Background
Most computer networked application architectures are organized as a series of layers, each layer built upon the one below it. The Open Systems Interconnect model is to have seven layers (L1-L7) in the system. Switching has historically taken place on Layers 2 and 3, with a recent emergence of Layer 4. In L2 switching, a local Media Access Control (MAC) address may be used to determine where to forward each packet. For this reason, L2 switching is not favored for large-scale networks such as the Internet or any LAN with more than two hundred and fifty nodes because of broadcast radiation issues.
L3 switching involves making a decision on where to forward each packet based on an IP (or similar) address located in the header of the packet. Due to its scaleability, L3 is currently the industry-standard for interconnecting networks and in the core of corporate LANs.
Layer 4 (L4) switching has been steadily gaining acceptance in the industry. L4 switching employs the information contained within the Transport Layer header to assist in switching and traffic handling. The L4 information indicates which protocol type is contained within each IP packet. Thus, L4 switching provides for several advantages: packet filtering, security, and quality of service. These are important features of L4 switching. However, the most crucial feature is server load balancing.
In server load balancing, a collection of physical servers, each with a different IP address, may support the same application service and be defined as a single virtual server. This virtual server becomes the single “logical server” with a single IP address. Therefore, rather than communicating directly with the real IP addresses of the physical servers, users direct traffic to the virtual server address.
In order to make this transition transparent to the user, a L4 switch may be used to direct the traffic to an appropriate server based on current traffic conditions. This also provides for the most effective use of the servers during high traffic conditions. FIG. 1 is a block diagram illustrating server load balancing. A server load balancer 2 in a L4 switch receives a syn packet from a user 4. The syn packet may have a destination address indicating the single virtual server. The server load balancer 2 then rewrites the destination address in the syn packet as one of the servers' 6a, 6b, 6c IP address. In doing so, it may attempt to balance the current traffic load evenly among the servers 6a, 6b, 6c. 
Layer 7 (L7), also known as application level switching, has been a goal of many companies for years. In L7 switching, the directing of packets may occur on a content level basis, where packets are directed to appropriate destinations based on the type of information they contain. Currently, some companies claim to have L7 switching capabilities, but their solutions involve routing packets based on destination IP address using a statically configured group of servers via a generic predictor algorithm. True L7 switching would allow content to be distributed throughout the Internet much in the same way some television programming is syndicated to individual stations rather than shown on a network.
FIG. 2 is a diagram illustrating a normal transaction involving a user's request for content. User 100 may wish to view content delivered by www.contentprovider.com. In order to do this, the user 100 must directly contact contentprovider.com's servers 102 to request the content. An IP syn packet must be sent to initiate a session, followed by an ack packet sent as a response contentprovider.com's servers 102. Then a request for content must be sent, followed by contentprovider.com's servers 102 returning the content to the user. Not only might this involve many “hops” on the Internet (and thus subject the request to traffic and other delays), but it also increases the danger of the user not being able to view the content, such as if contentprovider.com's servers 102 are down, or a switch 104 connected to its servers 102 is down.
If there was a solution that provided for true content-based routing, the content could be distributed at different points on the Internet and a direct connection to contentprovider.com's servers 102 need not occur. With the explosive growth of the Internet, it would be beneficial to have such a solution.